A newly assigned draft in Bitcoin's official BIP repository is proposing one of the ecosystem's most aggressive responses yet to the long-term quantum threat. BIP-361, titled Post Quantum Migration and Legacy Signature Sunset, would create a staged migration path that eventually makes legacy ECDSA and Schnorr spends invalid unless users move funds to a future post-quantum output type.

What the draft proposes

The text, merged into the bitcoin/bips repository on April 14, is still marked Draft and does not activate anything by itself. But it lays out a concrete timeline. In Phase A, starting about 160,000 blocks after activation, wallets could still spend from legacy scripts but new receives would need to go to post-quantum scripts. In Phase B, two years later, nodes would reject transactions that rely on legacy signatures, effectively freezing funds left on quantum-vulnerable outputs.

The draft also sketches a Phase C recovery path, still marked TBD, that could let some users reclaim frozen funds with a quantum-safe proof tied to a BIP-39 seed phrase.

Why it matters

The proposal is notable less because it is close to deployment, and more because it puts a hard deadline on Bitcoin's quantum migration debate. BIP-361 argues that over 34% of all bitcoin have already revealed a public key on-chain, making them future targets if large-scale quantum attacks become practical.

That framing is likely to stay controversial. The draft openly argues that preventing theft may justify rendering some old outputs unspendable, a tradeoff that cuts against Bitcoin's long-standing norm that valid keys should always control coins.